1. Field of the Invention
The present invention relates to an optical measuring device which irradiates a measurement object with light and measures a light amount distribution of light transmitted through or reflected on the object.
2. Description of Related Art
Conventionally, there has been used an optical measuring device configured to measure dimensions of an object, an interval between objects, a position of an object, a shape of an object, and the like by irradiating the object with light from a light source and by measuring a light amount distribution of light transmitted through or reflected on the object.
According to the optical measuring device described in JP 2002-277211 A, light emitted from a light source of a light projecting unit is diffused by a light diffusing unit and converted by a transmitter lens into substantially collimated light. The collimated light after the conversion is projected to a light receiving unit with a measurement object placed therebetween.
The light projected from the light projecting unit is converged by a first lens of the light receiving unit, passes through an aperture of a diaphragm, and produces an image on the light receiving surface of a CCD (charge-coupled device) image sensor by a second lens. The CCD image sensor outputs an analog output signal corresponding to an amount of the received light. An A/D converter of a controller converts the output signal of the CCD image sensor into a digital signal, and writes the digital signal in a data memory as received light amount data. A CPU (central processing unit) detects positions of edges of the measurement object based on the received light amount data stored in the data memory, and calculates a distance between the edges specified by the operation switch and outputs a result of the calculation.
According to the optical measuring device described above, the focus of the optical system of the light receiving unit from the first lens to the light receiving surface of the CCD image sensor is positioned between the transmitter lens of the light projecting unit and the first lens of the light receiving unit. If the edge of the measurement object is at the focus position of the optical system of the light receiving unit (hereinafter, referred to as a focused position), the received light amount in the received light amount distribution indicated by the received light amount data changes steeply at a portion corresponding to the edge position of the measurement object. Thus, it is possible to easily and correctly detect the edge position of the measurement object.
On the other hand, if the edge of the measurement object is displaced from the focused position, the received light amount in the received light amount distribution indicated by the received light amount data changes moderately at the portion corresponding to the edge position of the measurement object. In this case, it may not be possible to correctly detect the edge position of the measurement object. Therefore, when detecting the edge position of the measurement object, it is preferable to position the measurement object as close as possible to the focused position.
Whether or not the edge of the measurement object is at the focused position can be determined based on a ratio of change in the received light amount at the portion corresponding to the edge position of the measurement object in the received light amount distribution indicated by the received light amount data. However, it is not possible to determine whether the measurement object is on a side of the focused position closer to the light projecting unit, or on a side of the focused position away from the light projecting unit. In this case, it is difficult to move the measurement object toward the focused position. Therefore, it is not easily to improve accuracy in measurement of the edge position of the measurement object.